1. Field of the Invention
The present invention relates to the field of casting and molding machines, and more particularly to die casting machines of the automatic cast trim type whereby castings are formed and automatically punched from the spider.
2. Prior Art
Until recent years die casting machines were generally adapted to provide one or more die cast parts coupled to a spider formed by the flow paths supplying the die cast metal to the mold cavities. Such machines are characterized as having a stationary platen supporting one mold half and a movable platen supporting the other mold half, with an injector supplying the molten metal to the cavity when the two mold halves are closed. Typically the mold is designed so that the casting hangs up in one mold half, with ejector pins being provided to break the castings and spider loose from that mold half when the mold is opened. An operator would then reach between the mold halves to remove the casting, with the cast parts later being punched from the spider at a separate punch station and the spider remelted for recovery of the metal.
Recently new legal requirements, cost of labor and other considerations have resulted in the development and introduction of automatic cast trim machines whereby a single machine forms the casting and punches the cast parts from the spider automatically. In such machines the closed mold cavity is formed not only by two mold halves, but in addition by a support member typically in the sprue region at one edge of the mold so that the casting embraces the support member in some manner for support after separation of the casting from the mold. The support in turn is coupled to some form of index mechanism so that it may be rotated or otherwise transported through a series of stations, including a punch station for punching the cast parts from the spider, and a casting spider removal station for removal of the spider from the support member to complete the cycle.
Typical support members may include a single spud around which a part of the casting is formed, with the spider removal being achieved by simply forcing the casting off the end of the spud. Such a support member is disclosed in U.S. Pat. No. 3,547,181. This spud has certain advantages, including the fact that the casting entirely surrounds the periphery of the spud so that the shrinking of the casting during cooling provides firm locking pressure between the casting and the spud. Of course geometries other than purely round may be used to provide good angular indexing for rotation, if required, as in the foregoing patent. Similarly stripping of the spider from the spud may be positively accomplished, though in the foregoing patent the overall structure has the disadvantage of requiring removal of the casting in a direction which is orthogonal to the normal platen motion. Further, once the spider is stripped from the support spud in such a system, there is no convenient way of locating the spider with respect to any means for transporting the spider back to the pot.
Another type of automatic cast trim machine is that of my co-pending application, Ser. No. 352,126, entitled "Automatic Casting Machine ". This type of machine is of a horizontal structure rather than a vertical structure of U.S. Pat. No. 3,547,181, and has among its advantages the advantage that the relative location of the punch and die set may be reversed as desired so that the rotation of the spiders in a transverse axis is not required. While a casting support similar to that of the foregoing patent could be used, a simple basically two-dimensional casting support (neglecting the draft) allows for a simple punch-off of the spider as a normal application of the platen motion. The two dimensional support member also provides the advantage of allowing easy and automatic orientation of the casting spiders on a simple rail or track for guidance back to the pot.
The two dimensional support has a number of very substantial advantages. However, the two dimensional supports as were known prior to the present invention did not provide the rigidity desired, and sometimes required, of such devices. In particular, if the support is shaped so that the casting shrinks away from the support, the casting has the basic form of an open channel around the support, with the result that the channel sometimes opens up somewhat on shrinkage and indexing to result in undesired looseness between the casting and the support. If the support has an opening into which part of the casting is formed, the shrinkage of the casting tends to automatically result in some looseness of the casting on the support, and further, unless a large support is used so as to define a cavity taking a large amount of metal, the casting will be weak in this area and thus fail to provide the desired strength and rigidity.